This invention relates to a connector for anchoring a first building structural member to a second building structural member. The connector works in conjunction with a separate anchor member that is received by or is attached to the second building structural member and fastener means for attaching the connector to the first building structural member.
Earthquakes, hurricanes, tornadoes, and floods impose forces on a building that can cause structural failure. To counteract these forces, it has become common practice to strengthen or add ties between the structural members of a building in areas where such cataclysmic forces are typically focused. For example: framed walls can be attached to the foundation rather than merely rest on it; the connections between the framed walls of each floor can be strengthened; and joists can be connected to both their headers and the support member for their header. One of the most common connectors designed for strengthening structural connections is called a holdown by the inventor. Holdowns are commonly used to anchor framed walls to the foundation.
Early holdowns were constructed from two or more separate pieces of metal welded together. These holdowns had to be painted to prevent rusting. They were heavy and costly to produce.
State of the art holdowns are made from galvanized sheet metal formed on progressive die machines that require no welding or painting. See U.S. Pat. No. 4,665,672, granted May 19, 1987, to Commins, Gilb and Littleton; U.S. Pat. No. 5,092,097 granted Mar. 3, 1992, to Young; and U.S. Pat. No. 5,249,404, granted Oct. 5, 1993, to Leek and Commins. These advancements have reduced the cost of making holdowns while increasing their ability to withstand tension forces. However, recent severe earthquakes in San Francisco, Los Angeles, and Kobe, Japan, demonstrate that holdowns capable of being mass produced and installed inexpensively should be made even stronger for many connections.
All the holdown connectors of the prior art that work in conjunction with a separate anchor member work in a similar fashion. The anchor member, which is attached to the second structural member, attaches at the seat of the connector. This seat is connected to a back member. The back member attaches to the first building structural member, generally a stud in a framed wall. Most holdown connectors have one or more side members to increase the strength of the connector or to connect the seat member to the back member.
All prior art holdown connectors that attach to a separate anchor member share a common characteristic: they are formed with a planar or flat seat. Furthermore, the interfaces between the seat member and the back and side members are generally perpendicular.
When sufficiently strong tension forces are exerted on structural members attached to prior art holdown connectors, the seat of the connector will deflect, and the back member, and side members, if present, will bend inward, toward the attachment point of the seat with the anchor member. The action is somewhat analogous to pulling a slack rope taught. This deflection of the seat, back, and side members elongates the holdown connector, loosening the connection between the joined structural members. The effectiveness of the holdown is reduced.
Accordingly, there is a continuing need in the art for an improved connector that can be made inexpensively and installed easily, which better withstands forces imposed by cataclysmic events.